The present invention relates to power divider circuits, and more particularly to a low loss coplanar waveguide power divider circuit.
Known power dividers that provide low VSWR in coplanar waveguide balanced circuits rely on a Lange coupler type of configuration. A coplanar 90.degree. Lange coupler is an interdigital planar coupler, as described in "Interdigitated Coplanar Directional Couplers," E. M. Bastida, N. Fanelli, 1980 Electronics Letters, pages 645-646; "Interdigitated Stripline Quadrature Coupler," Julius Lange, IEEE Trans. MTT-IT, No. 12, 1150-1151, Dec. 1969. The disadvantage of the Lange coupler is that it has relative high loss.
Another type of 3 dB coupler is a Wilkinson coupler with one output a quarter of a wavelength longer than the other output. The 90.degree. Wilkinson is made by connecting an extra quarter wave length long (at center frequency) section of transmission line to the Wilkinson divider. Wilkinson couplers are described in "Microwave Circuit Analysis and Amplifier Design," S. Y. Liao, Prentice-Hall, Inc., Englewood Cliffs, N.J., 1987. However, this type of circuit is limited to microstrip implementations.
There is a need for a low loss coplanar waveguide 3 dB power divider for use in balanced circuits, and particularly such a power divider that has high isolation between output ports and low VSWR at the input port.